The trend to more sustainable and environmentally friendly products has directed the development of such composite products away from the use of formaldehyde based binders towards the use of formaldehyde-free binders. Among such formaldehyde-free binders, carbohydrate-based binders represent an important share.
In the context of this description, “formaldehyde-free” is understood to mean “comprising less than about 1 ppm formaldehyde based on the weight of the composition and not liberating substantial formaldehyde”.
Carbohydrate based binders include binders obtained by the reaction of a carbohydrate with a nitrogenous compound, such as Maillard-type binders, by the reaction of a carbohydrate with an organic acid, and other binders obtained from starting materials that include a carbohydrate.
Carbohydrates are readily available in nature. Sources are animal derived products such as chitosan (derived from crustacean shells) and plant derived products, including but not limited to starch, syrup, molasses and cellulose. These carbohydrates also called polysaccharides are macromolecules made up by saccharide units. An advantageous source of carbohydrate raw materials can be found in recycled materials, such as recycled municipal solid waste, recycled paper and/or sugar cane bagasse, and/or wood. Depending on the source and/or on the hydrolysis process used to degrade the polysaccharides, different polysaccharides or polysaccharide compositions may be obtained. In certain applications, smaller molecules may be preferred, such as short chain polysaccharides, oligosaccharides or even saccharide units. Again, depending on the source and/or hydrolysis process conditions, different saccharides or saccharide mixtures may be obtained. While cellulose hydrolysis will generate essentially C6 sugars, preferably C-6 reducing sugars, e.g. dextrose, hemicellulose will generate a large fraction of C5 sugars, like xylose for instance.
In raw materials resulting from hydrolysis of higher molecular weight carbohydrates, the level of C5-sugars or five membered ring sugars has been found to vary from 5 to 70 wt. %, preferably from 10, from 15, from 20 or even from 25% by weight, and up to preferably 60 wt. %, 50 wt. %, 45 wt. % or 40 wt. %.
It is known that saccharides may give rise to furfural and/or hydroxymethylfurfural formation in the course of the binder preparation and/or binder curing process. While starting from raw materials as discussed above to produce a binder may be of interest for several reasons, such as the availability of raw materials and costs of the manufacturing process, it has been found that the presence of C-5 sugars in the carbohydrate component gives rise to increased furfural and/or hydroxymethylfurfural generation in the course of the binder preparation and/or curing process. Furfural and/or hydroxymethylfurfural may be undesirable beyond a certain level, for environmental and/or health reasons, but also because of regulatory requirements. There is thus a need to reduce the level of furfural and/or hydroxymethylfurfural generated in the course of binder preparation and/or curing.